The RYB, CMYK, RGB, HSV and Hexadecimal Color

The RYB, CMYK, RGB, HSV and Hexadecimal Color Models

The RYB Color Model

? The red, yellow, and blue (RYB) primary colors became the foundation of color theories that described how artists mixed paint pigments to produce colors.

? These theories were summarized by Johann Wolfgang von Goethe (the famous German poet) in his document the Theory of Colors, published in 1810.

? In the late 19th century, German and English scientists established that a color model based on red, green, and blue (RGB) was better for describing human color perception because the cones in the human retina responded to these colors of light. The RGB color model is described below.

? The RYB Color Model is a subtractive system. A mixture of two primary colors is darker than the original colors. A mixture of all three primary colors should approximate black, although this is usually not precisely true.

? A popular theory in Europe during the late 18th century was that the harmony of a painting required colors with equal saturation. Bright red and blue colors existed (for example carmine and ultramarine), but no equally bright yellow. This motived a large effort among chemists to develop a good yellow pigment.

? Although the secondary colors orange and green can be created by mixing primary colors (orange = red + yellow and green = yellow + blue), the resulting colors are darker than the original primary colors; it is better to use orange and green pigments directly.

The CMYK Color Model

? Modern color printing prefers to use cyan, magenta, and yellow as primary colors instead of red, yellow and blue.

? Cyan, magenta, and yellow are the secondary colors on the RGB color wheel ? CYM is a subtractive system like RYG. ? Modern color printing systems use a four color system that includes black in addition to cyan,

magenta, and yellow. ? This system is called CMYK, where K represents the "key" color black. ? Black is used in addition to CMY for these reasons:

1. Black ink is cheaper than mixing C, M, and Y to obtain black. 2. Text printed in black has fine detail that would be blurred if printed with three different

colors. 3. A mixture of C, M, and Y produces an imperfect shade of black. 4. Soaking the page with three different inks produces a page that is slow to dry. ? To obtain white and light colors, halftoning is used. ? In addition to alternative to half-toning, the six-color system CMYKOG and the seven-color system CcMmYyK are used. (The colors c, m, and y are ligher versions of C, M, and Y.) ? Jacob Christoph le Blon (1667 - 1741) is credited with inventing the three-color (CMY) and fourcolor (CMYK) printing systems.

The RGB Color Model

? The RGB color model was first described by Thomas Young and Herman Helmholtz in their Theory of Trichromatic Color vision (first half of the 19th century) and by James Maxwell's color triangle.

? In addition to providing a good description of human color perception, the RGB model is the basis for displaying colors in television and computer screens.

? The RGB model is also used for recording colors in digital cameras, including still image and video cameras.

? The RGB model is an additive system. ? In practice, the RGB model must be modified to account for the characteristics of each device. In

many cases, the response of visual recording devices is nonlinear, which require some sort of gamma correction. ? To represent colors for a television or computer screen, each pixel of the screen is recorded as the triple (r,g,b) of numbers. One popular system uses numbers that range from 0 to 255 for each color. ? Examples:

The HSV Color Model

? When artists began to use computers for graphic design, it was soon discovered that the RGB system is not a very intuitive way to represent colors.

? Alvy Ray Smith in 1978 was the first to describe colors using hue, saturation, and value (HSV model). Hue is a saturated color Saturation is the amount of white added to the color. 0% means that the color (at V=100%) is totally white; 100% means totally saturated with no white added (a fully saturated color is a pure hue on the outer rim of the HSV color wheel). Value is the brightness of the color. 0% means totally dark or black; 100% means full brightness, with the color is fully determined by the hue and saturation.

? Graphic artists like the HSV color model because it is an intuitive way to modify the colors in a region of an image. For example: Add more green to a region translates to "rotate the hue towards 120 degrees." Make the color more of a pastel color translates to "decrease the saturation." Make the colors in the image darker translates to "decrease the value."

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